1. Field of the Invention
The present invention relates to a construction of an electronic device such as an image-forming device equipped with a wireless unit board, such as a wireless LAN board, for transmitting and receiving a radio signal to and from external equipment.
2. Description of the Related Art
In recent years, with progress of networking in offices and homes, and with realization of wireless data communication as fast as wired data communication or even faster by adopting IEEE 802.11 as a standard specification for a wireless LAN system, development of electronic devices, such as personal computers (hereinafter referred to as PCs), that can conduct data communication using the wireless LAN system is feverishly conducted.
An example of methods for using a wireless LAN is to externally connect an adapter provided as a wireless LAN card disclosed in Japanese Patent Application Laid-Open No. 2002-344172 (see FIG. 1) to an electronic device such as a PC or a printer. Another example is to provide a wireless LAN board in the electronic device. For example, Japanese Patent Application Laid-Open No. 2001-290558 (see FIGS. 1 and 2) discloses that a wireless LAN board (also called as a wireless LAN unit) is provided on a rear side of a front panel of a main unit case of an electronic device so as to reduce time and effort for external wiring as well as an installation space. Further, Japanese Patent Application Laid-Open No. 2000-184316 (see FIGS. 2, 4, and 9) discloses a wireless LAN board (also called as a wireless LAN card) provided inside a main unit case of a projection display apparatus (projector).
Radio waves to be used for the IEEE 802.11a/g standard are in a 2.4 GHz band, and those to be used for the IEEE 802.11a standard are in a 5 GHz band. Accordingly, a circuit unit such as a CPU operating at maximum frequencies and mounted on a main control board of the electronic device is susceptible to electromagnetic noise caused by such radio waves transmitted from an antenna of the wireless LAN board. There has also been a problem that a circuit unit (wireless module) on the wireless LAN board and a harness (wiring) connecting the wireless LAN board to the main control board are subject to electromagnetic noise, when they are in the vicinity of a power board with strong magnetic field lines.
Therefore, in Japanese Patent Application Laid-Open No. 2002-344172, a circumference of the wireless LAN board is shielded with upper and lower plate covers, and in Japanese Patent Application Laid-Open No. 2001-290558, a through hole is provided at a portion of a substrate of the wireless LAN board, in a thickness direction of the substrate, where no ground pattern is formed, and a conductor in the through hole is connected to one end of a wire line which passes through the substrate and is connected to the circuit unit (wireless module) of the wire line. Further, in Japanese Patent Application Laid-Open No. 2000-184316, a plating film is formed on an area of an inner surface of an upper cover of the electronic device so as to face a part of the wireless LAN board excluding the antenna, and the remaining area of the inner surface of the upper cover that faces the antenna constitutes an uncovered area as an area through which radio waves pass.